1. Technical Field of the Invention
The present invention relates to a process-independent thermal protection circuit for microelectronic circuits.
2. Description of Related Art
It is known that microelectronic circuits are provided with thermal protection in order to protect their operation if the temperature rises above a predetermined threshold temperature.
These thermal protection circuits generally use the temperature-dependent variation of an implantation resistor, coupled to the variation of a voltage between the base and the emitter of a bipolar transistor.
The coupling can be direct, i.e., the resistor is connected between the base and the emitter of the bipolar transistor. FIG. 1 illustrates a direct coupling configuration, in which resistor RT is the resistor coupled between the base and the emitter of the bipolar transistor 1.
FIG. 2 shows an example of an indirect coupling configuration, in which a comparator 2 detects the positive variation of the voltage on one side caused by the resistor RT, and the negative variation on the other side caused by one or more diodes 3 and 4.
Usually, especially in processes with high production capacities, control of process-related characteristics is unreliable, resulting in the resistance of resistor RT varying considerably between different batches and throughout the years of product production. Statistical estimates confirm resistance variations on the order of plus or minus 10%.
Moreover, two or three tests with different contacts are usually performed in order to calibrate a thermal protection. These tests slow the development of the device, especially when this is done by using lines which are not dedicated to development.